The present invention relates to a method for fabricating an organic thin film that will serve as a resist film, an anti-reflection film or the likes.
As the systems bearing complex semiconductor integrated circuits have been downsized, it is becoming increasingly difficult to print complex circuit patterns onto a small semiconductor chip by the pattern lithography method that uses a resist pattern, namely, a patterned resist film, as a mask. As the wavelength of the energy beam used in the pattern lithography method becomes shorter, the beam which has passed through the photosensitive organic film serving as a resist film is reflected at higher reflectivity off the surface of the film to be etched (formed under the resist film). Then, undesired areas in the photosensitive organic film (the areas which should not be irradiated with the energy beam) other than the target areas for exposure may be subject to unintentional exposure.
To solve this problem, a method for reducing the reflection of the energy beam that has passed through the photosensitive organic film has been proposed in which an organic film that absorbs the energy beam is coated on the film to be etched as an anti-reflection film prior to the formation of the photosensitive organic film serving as a resist film.
FIGS. 9A and 9B are sectional views illustrating steps of an organic thin film fabrication method according to the prior art.
Referring now to FIG. 9A, the semiconductor substrate 100 on which a film to be etched (not shown) has been formed is first subjected to wet-cleaning to remove particles that have stuck on the surface of the semiconductor substrate 100 when the film to be etched is formed, for example. To be more specific, the semiconductor substrate 100 is turned while a cleaning liquid 102 is supplied from a nozzle 101 onto the semiconductor substrate 100.
Next, as shown in FIG. 9B, an organic film 103, which will serve as a resist film or an anti-reflection film, is formed on the semiconductor substrate 100 of which wet-cleaning has been completed.
As the design rule for electronic devices becomes increasingly fine in recent years, it has become hard to form fine resist patterns when the photosensitive organic film serving as a resist film is thick. Besides, if the organic film serving as an anti-reflection film is thick, the resist film is subjected to undesired etching. To solve such a problem and enable to provide fine resist patterns, a few methods have been proposed for forming a thin organic film serving as a resist film or an anti-reflection film.
At least the same or higher levels of uniformity in film thickness are required in forming an organic thin film, compared with the case of forming an organic thick film.
Then it is necessary to increase the content of solvent in the organic material used in forming the organic thin film, in order to make viscosity of the organic material low. However, if the content of solvent in the organic material is raised, the uniformity of film thickness is more likely to be affected by the heat of vaporization of solvent (Japanese Patent Laid-Open Publication No. Hei. 8-186072).
In addition to the above-mentioned drawback, the inventors of the present invention have found another problem that if an organic thin film is formed 100 nm or less in thickness on a silicon nitride film or silicon nitride oxide film that is deposited as a hard mask or an inorganic anti-reflection film, a coating pattern running radially from the wafer center to its peripherals shows up (hereafter, coating unevenness) on the fabricated organic thin film. An organic thin film that has such coating unevenness cannot be used as a resist film or an anti-reflection film.
In view of the foregoing, it is, therefore, an object of the present invention to provide a method for forming organic thin films, using an organic material of a low viscosity, of uniform thickness and free of such coating unevenness, when forming an organic thin film onto the silicon nitride film or silicon nitride oxide film.
In order to attain the above object, a first method for fabricating an organic thin film according to the present invention comprises the steps of: forming an undercoating film made of silicon nitride or silicon nitride oxide on a substrate; wet-cleaning the undercoating film using a cleaning liquid; irradiating far ultraviolet ray onto the undercoating film of which wet-cleaning has been completed; and forming an organic thin film with a thickness of about 100 nm or thinner on the undercoating film onto which far ultraviolet ray has been irradiated by turning the substrate and providing a liquid organic material onto the substrate.
According to the first method for fabricating an organic thin film of the present invention, the undercoating film made of silicon nitride or silicon nitride oxide is wet-cleaned; far ultraviolet ray is irradiated onto the undercoating film; and then the organic thin film with a thickness of about 100 nm or thinner is formed on the undercoating film. Then compared with the conventional organic thin film fabrication method that conducts no irradiation of far ultraviolet ray onto the undercoating film, coating unevenness is unlikely to show up in the resulting organic thin film even when an organic material of low viscosity is employed. Therefore, the uniformity of thickness of the organic thin film can be improved. When the organic thin film is formed as a resist film or anti-reflection film, it becomes possible to make fine resist patterns. Then it becomes also possible to provide electronic devices of finer design rules.
A second method for fabricating an organic thin film according to the present invention comprises the steps of:
forming an undercoating film made of silicon nitride or silicon nitride oxide on a substrate; wet-cleaning the undercoating film using a cleaning liquid; and forming an organic thin film with a thickness of about 100 nm or thinner on the undercoating film, of which wet-cleaning has been completed, by turning the substrate and providing a liquid organic material onto the substrate; wherein the organic material contains at least one solvent selected from the group consisting of propylene glycol monomethyl ether acetate, propylene glycol monomethyl-ether, ethyl lactate, ethyl methoxy propionate, ethyl ethoxy propionate, 2-heptanone, ethyl pyruvate, diethylene glycol monomethyl ether, methyl cellosolve acetate, propylene glycol monoethyl ether acetate, ethyl methoxy propionate, methyl lactate and methyl pyruvate.
According to the second method for fabricating an organic thin film of the present invention, the undercoating film made of silicon nitride or silicon nitride oxide is wet-cleaned and then organic thin film with a thickness of about 100 nm or thinner is formed on the undercoating film by the use of an organic material containing at least one solvent selected from the group consisting of propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, ethyl lactate, methyl methoxy propionate, ethyl ethoxy propionate, 2-heptanone, ethyl pyruvate, diethylene glycol monomethyl ether, methyl cellosolve acetate, propylene glycol monoethyl ether acetate, ethyl methoxy propionate, methyl lactate and methyl pyruvate. Then, compared with the conventional organic thin film fabrication method that does not use an organic material containing the above solvent, coating unevenness is unlikely to show up in the resulting organic thin film even when an organic material of low viscosity is employed and therefore the uniformity of the thickness of the organic thin film can be improved. When the organic thin film is formed as a resist film or anti-reflection film, it becomes thereby possible to make the resist pattern finer. Then it also becomes possible to provide electronic devices of finer design rules.
Further, compared with the first method of the invention, the second method does not need the irradiation process of far ultraviolet ray onto the undercoating film. As a result, the organic thin film fabrication process can be simplified and its processing time can be shortened.
In the first and second organic thin film fabrication methods, the step for wet-cleaning preferably includes a step of applying ultrasonic wave in the cleaning liquid.
Then particles that have stuck on the surface of the undercoating film during the formation of the undercoating film can be reliably removed.
In the first and second organic thin film fabrication methods, it is preferable to insert a step of forming another organic thin film on the undercoating film and then removing this organic thin film between the step of forming the undercoating film and the step of wet-cleaning.
Then residues that have stuck on the surface of the undercoating film during the removal of another organic thin film can be removed reliably by the wet-cleaning.
A third method for fabricating an organic thin film according to the present invention comprises the steps of:
forming an undercoating film made of silicon nitride or silicon nitride oxide on a substrate; irradiating far ultraviolet ray onto the undercoating film;, and forming an organic thin film with a thickness of about 100 nm or thinner on the undercoating film onto which far ultraviolet ray has been irradiated by turning the substrate and providing a liquid organic material onto the substrate; wherein the organic material contains at least one solvent selected from the group consisting of propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, ethyl lactat6, methyl methoxy propionate, ethyl ethoxy propionate, 2-heptanone, ethyl pyruvate, diethylene glycol monomethyl ether, methyl cellosolve acetate, propylene glycol monoethyl ether acetate, ethyl methoxy propionate, methyl lactate and methyl pyruvate.
According to the third method for fabricating an organic thin film of the present invention, after far ultraviolet ray is irradiated onto the undercoating film made of silicon nitride or silicon nitride oxide formed on the substrate, an organic a thin film with a thickness of about 100 nm or thinner is formed on the undercoating film by the use of an organic material containing at least one solvent selected from the group consisting, of propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, ethyl lactate, methyl methoxy propionate, ethyl ethoxy propionate, 2-heptanone, ethyl pyruvate, diethylene glycol monomethyl ether, methyl cellosolve acetate, propylene glycol monoethyl ether acetate, ethyl methoxy propionate, methyl lactate and methyl pyruvate. Then compared with the conventional organic thin film fabrication method that does not conduct far ultraviolet ray irradiation on the undercoating film or use an organic material containing the above solvent, coating unevenness is unlikely to show up in the organic thin film even when an organic material of low viscosity is employed. Therefore, the uniformity of thickness of the organic thin film can be improved. When the organic thin film is formed as a resist film or anti-reflection film, it becomes possible to make fine resist patterns. Then it becomes also possible to provide electronic devices of finer design rules.
Further, compared with the first method of the invention, the third method does not need the wet-cleaning process for the undercoating film. As a result, the organic thin film fabrication process can be simplified and its processing time can be shortened.
In the first and third fabrication methods, the step of irradiating far ultraviolet ray preferably includes a step of performing heat treatment on the substrate.
Then it becomes possible to reliably prevent the occurrence of coating unevenness in the organic thin film.
In the first, second and third methods, it is preferable to make the total amount of the organic material used in the step of forming the organic thin film at least 0.8 ml.
Then uniformity in the thickness of the resulting organic thin film can be further improved.